The invention concerns a method for the open-loop and closed-loop control of a V-type internal combustion engine with an independent A-side common rail system and an independent B-side common rail system, in which the speed of the internal combustion engine is automatically controlled in a closed-loop speed control system.
In an internal combustion engine with a common rail system, the quality of combustion is critically determined by the pressure level in the rail. Therefore, in order to stay within legally prescribed emission limits, the rail pressure is automatically controlled. A closed-loop rail pressure control system typically comprises a comparison point for determining a control deviation, a pressure controller for computing a control signal, the controlled system, and a software filter in the feedback path for computing the actual rail pressure from the raw values of the rail pressure. The control deviation is computed as the difference between the set rail pressure and the actual rail pressure. The controlled system comprises the pressure regulator, the rail, and the injectors for injecting the fuel into the combustion chambers of the internal combustion engine. For example, DE 103 30 466 B3 describes a common rail system of this type, in which the pressure controller acts by means of a control signal on a suction throttle arranged on the low-pressure side. The suction throttle in turn sets the admission cross section to the high-pressure pump and thus the volume of fuel delivered.
DE 10 2007 034 317 A1 describes an internal combustion engine with an A-side and a B-side common rail system, which are identical in structure. The two common rail systems are hydraulically decoupled from each other and therefore allow independent closed-loop control of the A-side and B-side rail pressure. Pressure fluctuations in the rails are reduced by the separate closed-loop control. Correct closed-loop rail pressure control requires properly operating rail pressure sensors. The failure of one rail pressure sensor or both rail pressure sensors in a given system results in an undefined state of closed-loop pressure control and can produce a critical state of the internal combustion engine, since the cited document fails to indicate any fault safeguards.
The unprepublished German patent application with the official file number DE 10 2008 036 300.6 also describes an internal combustion engine with an independent A-side common rail system and an independent B-side common rail system and closed-loop speed control. In the closed-loop speed control system described there, a speed controller uses the speed control deviation to determine a set torque, which is limited to a maximum value. The maximum value is computed as a function of the actual speed, the charge air pressure, and an air mass ratio. A set injection quantity is then computed by an efficiency input-output map as a function of the limited set torque. An injector input-output map then uses the set injection quantity and a rail pressure to compute the injection time for the actuation of an injector. If an A-side injector is to be actuated, the A-side actual rail pressure is used as the input variable of the injector input-output map. If a B-side injector is to be actuated, the B-side actual rail pressure is used as the input variable of the injector input-output map. Switching from the A side actual rail pressure to the B-side actual rail pressure is carried out as a function of the firing order. Therefore, the failure of a rail pressure sensor causes an undefined state.
During the start-up process, a large speed control deviation is present, since, for example, the idle speed value of 600 rpm is preset as the set speed, while the actual speed corresponds to the starter speed of 120 rpm. Due to the large speed control deviation, the speed controller computes a very high set torque, so that an injection is electrically initiated. The physical opening pressure of the injection nozzles is in the range of 300 to 350 bars. This means that the injection nozzles do not open until the rail pressure reaches or exceeds this pressure threshold. If the rail pressure is less than the nozzle opening pressure, the injection nozzles stay closed, even if the injectors are energized. However, a suitable control quantity of fuel is taken by the injector from the supply line from the rail by the electric actuation of the injectors. The removed control quantity causes a delayed pressure buildup in the rail and causes a delayed start-up process.